The present invention relates to a small-size motor which is suitable for rotating CD, DVD, MD, or CD-ROM, DVD-ROM, and other various types of information recording discs (referred to simply as xe2x80x9cdiscsxe2x80x9d), and applicable to other various uses.
An example of a disc drive motor is shown in FIG. 8. As shown, a motor 60 is generally composed of a stator section 64 and a rotor section 65. The stator section 64 includes a base board 64a, a sintered oil-contained bearing 64b fastened to the base board 64a, a stator core 64c which is fastened to the outer circumferential face of the sintered oil-contained bearing 64b while being arranged coaxially with the bearing, and a coil winding 64d wound around protruding poles of the stator core 64c. 
The rotor section 65 includes a rotary shaft 65b rotatably supported with the aid of the sintered oil-contained bearing 64b, a cup-shaped rotor case 65c which is coupled to the rotary shaft 65b so as to rotate together with the latter, and an annular rotor magnet 65d fastened to the inner circumferential face of the rotor case 65c. 
A thick, annular boss 67 with a disc-like flange 67a formed therearound is fitted into the central portion of the rotor case 65c. The rotary shaft 65b is press-fitted into a center hole of the annular boss 67. With this structure, the rotor case 65c is coupled to the rotary shaft 65b with the annular boss 67 intervening therebetween, whereby the rotor case and the rotary shaft are rotated together.
A tapered portion 67b is formed around the lower end of the center hole of the annular boss 67. The tapered portion 67b is formed so as to assist the press-fitting of the rotary shaft 65b into the center hole of the annular boss 67.
A chucking mechanism 63 is provided around a portion of the rotary shaft 65b, which is extended above the upper face of the rotor case 65c.The chucking mechanism 63 is generally formed with a fitting member 68 to be fitted into the center hole of the disc, clamping members 69 provided at a plurality of locations on the outer circumferential face of the fitting member 68, and a plurality of urging members 70 for radially urging the clamping members 69 respectively.
Some recent technical requirements are to thin the motor and to improve a shock resistance of the motor. This necessitates increase of a coupling force of the rotary shaft 65b to the annular boss 67.
A possible approach to increase the coupling force of the rotary shaft 65b with the annular boss 67 is to increase a length xcex1 of the center hole of the annular boss 67 as viewed in the axial direction as shown in FIG. 9. However, this coupling-force increasing approach is defective in that if the length xcex1 of the center hole of the annular boss 67 is increased, it is impossible to thin the motor.
Another possible approach to increase the coupling force is that the inside diameter of the center hole of the annular boss 67 is selected to be smaller than the outside diameter of the rotary shaft 65b, and an overlap width of press-fitting of the rotary shaft to the boss is increased. However, this approach is defective in that it is difficult to secure the perpendicularity of the rotary shaft to the boss at the time of the press fitting, and it will cause the perpendicularity of the boss to degrade.
A further possible approach is that a groove is formed around the outer circumferential face of the rotary shaft 65b where it is in contact with the center hole of the annular boss 67, and is filled with adhesive, whereby the rotary shaft 65b is bonded to the center hole of the annular boss 67. However, this approach is defective in that the workability is impaired, and the coupling force of the rotary shaft 65b to the annular boss 67 varies depending on a variation of the amount of adhesive.
The coupling of the rotary shaft 65b with the annular boss 67 by welding also suffers from problems of cost increase and limitation of a kind of material that may be used.
Generally, a sintered oil-contained bearing is used for the bearing of the motor. As shown in FIG. 8, the sintered oil-contained bearing 64b is impregnated with lubricant oil. The lubricant oil fills a gap between the inner circumferential face of the sintered oil-contained bearing 64b and the outer circumferential face of the rotary shaft 65b. With presence of the lubricant oil, the rotary shaft 65b is smoothly rotatable. The lubricant oil in the gap oozes from the upper end of the sintered oil-contained bearing 64b. In the thinned motor, the exuded lubricant oil is likely to reach the lower end of the boss 67. When the oil reaches the lower end of the boss 67, part of the lubricant oil is radially splashed along the end face of the boss 67 by a centrifugal force generated.
The splashing of the lubricant oil results in reduction of the amount of the lubricant oil in the gap, and hence in reduction of the lifetime of the bearing. Further, the splashed oil soils related parts of the motor. A gap between the upper end of the sintered oil-contained bearing 64b and the end face of the annular boss 67 may be increased so as to prevent the lubricant oil oozing from the upper end of the sintered oil-contained bearing 64b from reaching the boss 67. In this case, a dimension of the motor in the axial direction is increased. This fact makes it impossible to thin the motor.
The present invention is made to solve the problems of the related techniques, and has a first object to provide a small-size motor which is capable of improving the perpendicularity of the boss to a shaft to achieve the thinning of the motor.
The invention has a second object to provide a small-size motor which, to thin the motor, prevents the splashing of the lubricant oil and impregnates again the sintered oil-contained bearing with the oozing lubricant oil.
In order to achieve the above objects, according to the present invention, there is provided a motor comprising:
a boss having a center hole; and
a shaft press-fitted into the center hole, a diameter of which is A,
wherein a tapered portion is formed around one end of the shaft, which is inserted to the center hole, such that a dimension in the extending direction of the shaft is R; and
wherein the boss includes a cylindrical recess formed concentrically with the center hole on one end face thereof facing a side from which the shaft is inserted such that a dimension in the extending direction of the center hole thereof is larger than R, and such that a diameter thereof is A less than Bxe2x89xa61.05A.
Preferably, the cylindrical recess includes a first side wall linearly extending from the end face of the boss and a second side wall subsequent to the first side wall, which is tapered inwardly in order to serve as an insertion guide member against which the tapered portion of the shaft is to be abutted when the shaft is inserted into the center hole.
With this structure, the perpendicularity of the shaft to the boss is secured when the shaft is press-fitted into the boss, without increasing the axial length of the center hole of the boss, whereby motor may be thinned.
Preferably, a caulking member is provided on at least one end face of the boss so as to surround the center hole, which is to be compressed onto the shaft inserted into the center hole.
When comparing the motor structure in which the shaft is simply press-fitted into the center hole of the boss, a coupling force of the shaft with the boss may be increased without increasing the axial length of the center hole of the boss. Therefore, thinning of the motor and improvement of the motor shock resistance are both achieved.
According to the present invention, there is also provided a motor comprising:
a boss having a center hole;
a shaft press-fitted into the center hole;
a sintered bearing for supporting the shaft, in which lubricant oil is contained;
a holder for holding the bearing; and
a wall member formed on one end face of the boss so as to face the bearing with a gap having a predetermined width in between for blocking the lubricant oil splashed from the bearing.
Preferably, the blocking wall member extends in a direction of which the center hole extends so as to surround an outer circumferential face of the bearing. The gap between the blocking wall member and the outer circumferential face of the bearing is determined to such an extent that the splashed lubricant oil attached to the blocking wall and depended therefrom can adhere again onto the outer circumferential wall of the bearing.
Therefore, if the lubricant oil reaches the end face of the boss, the blocking wall member prevents the lubricant oil from splashing to the related portions of the motor. If the blocking wall member is formed on the boss so as to confront with the upper end face of the bearing. The dimension between the upper end of the bearing and the end face of the boss is reduced, and hence the thinning of the motor is achieved.